1. Field of the Invention
The present invention relates to a fuel injection pump with a cold start device for advancing fuel injection to a diesel engine when being started up in a low temperature, and particularly, to a technology for optimizing the fuel injection timing and quantity during the engine start-up in a low temperature.
2. Background Art
Conventionally, there are well-known fuel injection pumps for diesel engines, each comprising a plunger, a plunger barrel, a distribution shaft, and delivery valves, wherein the plunger is vertically reciprocated in the plunger barrel to discharge compressed fuel to the distribution shaft, the distribution shaft distributes the fuel from the plunger among the delivery valves, and the delivery valves deliver fuel to respective fuel injection nozzles.
Some of the well-known fuel injection pumps each includes a device for advancing fuel injection to a diesel engine when being started up in a low temperature (“Cold Start Device,” hereinafter referred to as “CSD”), wherein the CSD operates an injection-advancing actuator for opening or closing an overflowing sub port formed in the plunger barrel so as to change the injection timing. As disclosed in Japanese Laid Open Gazette No. 2000-234576, when the engine is started up in a low temperature, the CSD is activated to close the overflowing sub port so as to advance the fuel injection timing, thereby optimizing the start-up of the engine.
When the CSD is activated for injection-advancing, the injection-advancing actuator actuates a piston for closing the overflowing sub port which is opened in a normal temperature. Accordingly, the discharge of compressed fuel from a fuel compression chamber to the distribution shaft is started immediately the plunger shuts off a main port from the fuel compression chamber.
However, with respect to the conventional fuel injection pump, the change degrees of the advanced injection timing and quantity during closing of the overflowing sub port (activation of the CSD) from those during opening of the overflowing sub port (inactivation of the CSD) are univocally decided depending on the positional setting of the overflowing sub port in the plunger barrel relative to the main port and depending on the diameter size of the overflowing sub port. This is the reason why optimization of the engine start-up during activation of the CSD (in a low temperature or a cold engine condition) while ensuring the require engine performance during activation of the CSD (in a normal temperature or a warmed engine condition) is difficult.